GROUPS OF PLANTS. 



19 



ridinm is more or less cylindrical and contains a somewhat uni- 

 form mass of protoplasm. The antheridium bends toward the 

 oogonium and comes in contact with it, but apparently does not 

 in all cases penetrate it. Nevertheless the egg-cells develop walls 

 and become resting oospores. 



Fig. II. Species of Saprolegnia. A, mycelium growing out from and surrounding 

 a dead house-fly in a water culture; B, C, sporangia with biciliate swarm spores; D, a 

 number of oogonia containing oospheres; E, F, oogonia and antheridia, in F the tube of 

 the antheridium having penetrated the oogonium. A-C, after Thuret; D-F, after 

 De Bary. 



In Peronospora^ one of the Oomycetes, the antheridium 

 (Fig. 12, n) develops a tube which pierces the wall of the 

 12, 0) \ the contents unite with the egg-cell, 



oogonium ( Fi 



after which a heavy membrane develops forming an oospore 

 which germinates when it finds a suitable host. The plants 

 belonging to Peronospora as well as related genera are destruc- 



